The spectral (or eigen) gap of a graph is the absolute difference between the biggest and second biggest eigenvalue of the adjacency matrix. To compare spectral gaps across networks, the fraction can be used.
spectral_gap(g, method = "frac")igraph object
A string, either "frac" or "abs"
Numeric value
The spectral gap is bounded between 0 and 1 if method="frac". The closer
the value to one, the bigger the gap.
# The fractional spectral gap of a threshold graph is usually close to 1
g <- threshold_graph(50, 0.3)
spectral_gap(g, method = "frac")
#> [1] 0.7891508